The present invention relates to a disc drive microactuator system and more particularly to an improved structure for increased stability of the microactuator rotor.
The density of concentric data tracks on magnetic discs continues to increase (that is, the width of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the transducing head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor, to radially position a slider (which carries the head) on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks.
One particular design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby effecting head positioning through dual stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. In particular, magnetic microactuator designs featuring a magnet/keeper assembly and coil have been developed. Magnetic microactuators typically include a stator portion and a rotor portion, the stator being attached to the flexure and the rotor supporting the slider. The rotor is movable with respect to the stator such that the slider can be positioned more precisely over a track of a disc.
Some existing magnetic microactuators use flexible beam springs in a “wagon wheel” design located on top of the slider to support the rotor. The beam springs have a limited thickness, generally 20 to 30 microns, with their thickness being constrained by the total microactuator thickness. Thin beam springs are highly stressed by normal disc drive loads, such as head slap deceleration. During head slap deceleration, a load in a disc drive causes the suspension, microactuator and slider to lift off the disc momentarily and then crash back into the disc surface with a very high deceleration, sometimes approaching 600 gravities (g). Under 600 g, the flexible beam springs bear a weight of 0.1 Newton (N). The force applied during head slap deceleration induces high stress in the flexible beam springs.
Prior art designs utilizing a linear accessing motion suffer from uncontrolled rotor shifting caused during hard seek acceleration of the voice coil motor (VCM). The large shift in rotor position stresses the beam springs to approximately 8.8% of their breaking strength and because of the time-varying nature of the VCM acceleration induces fatigue failure. There is a need in the art for an improved microactuator beam structure to increase the rotor stability.